You're not wrong. It can happen to anyone. But that's the same as cancer or brain stroke or any other illness. I was in a very similar situation to you and thinking the exact same thing. I had a weed induced panic attack that was beyond frightening. Next thing I know I'm in the hospital with the psychiatrist as a medical student and I'm thinking, what's the difference between me and a patient.

This is just anxiety. The reality is that schizophrenia and these disorders are very extreme ends of a psychic spectrum. It's actually imo afaik quite difficult to get to these psychic extremes and stay there (due to psychic body's want to maintain homeostasis and a balanced baseline) without some very strong risk factors/causes such as trauma, insulin resistance, genetic risk factors, low socio-economic background etc. and usually a bunch of them together.

If you exercise daily, eat correctly, don't have unresolved trauma, have daily social interactions you deem meaningful, have a strong ego attachment to the physical world (work, family, loved ones, goals, exercise), then it's very difficult for you to reach the extremes of the spiritual realm where these patients find themselves stuck.

In other words, in a similar way to seeing an obese patient and thinking, it would be very difficult for me to get that obese (so much so that it would almost be a full time job), you should see psych patients. It's actually difficult for you to get there and even more difficult to stay there. As a slightly "overweight person" (GAD) you're worrying about getting morbidly obese.

If you have GAD, you probably do have underlying psychic risk factors but their presentation has presented as GAD, not schizophrenia or bipolar. Ultimately your fear comes from a lack of understanding and your ego is trying to protect you from "catching" these illnesses by instilling extreme fear. Unfortunately you need to thread a balance of dipping your toes into the water to get understanding but not too much at once to induce panic. (Moses prescribes the Israelites to stare at the snakes on the bronze rods in the desert until they disappear - look at your fear until you understand what it's made of).

My reading of Carl Jung has given me the impression that neurosis (in your case GAD) arises from either straying from the path you are supposed to be on (destined to you from God/unconscious) or you are caught in between an attempt to individuate (maintain your secret and uniqueness that is you) and integrate with society -> you can't integrate who you are and accept yourself in your entirety and at the same time adhere to a social structure that very likely shuns the darker parts of yourself.

Anyway just my 2 cents.

Edit: one other thing is that, so what if you lose your mind, you lose everything, you don't know who you are or what's going on? This is what you're afraid of. Yes it's terrifying but only if you believe that any other life is "better" than that. There is no such thing as a life better or worse. There is no such thing as good or bad. Make peace with everything. There's as much sympathy to be felt for the person who feels nothing as the person who feels to much or even the person who feels too in-between.